Several torque converter transmissions, with planetary gearing arrangements, have been disclosed heretofore, such as U.S. Pat. Nos. 3,150,542, 3,528,321, and 3,789,697. Although differences exist in construction, they do have a common feature in that the impeller of the torque converter is connected to the input shaft and driven directly by the prime mover in such a way as to rotate with the same speed as the input shaft; therefore, when the vehicle is starting, or in low speed condition, the torque transmitted from the impeller to turbine is limited by the rotational speed. Higher stall-torque-ratio and transmission efficiency thus cannot be achieved.
Moreover, all the converters mentioned above are of a purely hydraulic type, having no mechanical bypass with low efficiencies, due to fluid splippage. Furthermore, when the engine is slowed down, or the vehicle is moving on a down-grade, the backward torque transmission capacity is small because of the small speed difference between impeller and the turbine and the absence of mechanical linkage.
In U.S. Pat. Nos. 3,425,295 and 3,503,277 the converters have both mechanical and hydraulic torque transmission paths; however, they are not effected in parallel. Purely hydraulic transmission occurs at low speed and purely mechanical transmission occurs in the high speed range. In U.S. Pat. No. 3,628,321 hydraulic and mechanical transmissions are used in parallel but only in high speed range. The aforementioned inventions all use clutches to change the modes of operation.
The invention disclosed in U.S. Pat. No. 3,163,056 employs parallel path transmission, but it does not use regenerative torque multiplication and the torque ratio is in fact reduced.
This invention eliminates the aforementioned drawbacks and brings about advantages never realized before.